There's more to Fantasy than a single boolean "does it contain something that is not real?"

Fantasy gets applied to the work as a whole, to its dominant tone and structure, not to one element. A work of fantasy usually has other elements that show it to be such. Is there world-building? Is it a quest or a hero story? Is there some kind of lore that grounds the whole universe? Not all of those are necessary, but usually you can clearly define the whole work holistically as Fantasy.

From Dusk till Dawn in particular is a straight crime thriller that turns into a horror movie.

Ok, I got nerd-sniped into trying to define Fantasy after saying I wouldn't.

Vampires aren't any more fantastical than FTL travel, and yet we're perfectly happy to have that in SF.

I'd say that line can be blurred somewhat by "Blindsight". "Not real" isn't where I'd put the line, it's "not plausibly and consistently explained (or at least explained away) within the laws of nature.